(a) Field of the Invention
The present invention relates to a shift lens system arranged to move the lens system in the direction parallel with the image surface and having a correcting means arranged to correct aberrations favourably when the lens system is shifted.
(B) Description of the Prior Art
Lens systems generally called shift lens systems are arranged to obtain the shift effect by moving the lens system as a whole in the direction parallel with the image surface. By arranging as above, it is generally possible to photograph a range of object of a field angle which is apparently larger than the field angle determined by the film size and, for the image obtained at that time, variation of magnification of image is not caused. However, the image circle for which it is possible to focus an image by the shift lens should be large enough to obtain satisfactory shift effect. For this purpose, the included field angle of the lens system should be made extremely large and this causes very large difficulty for correcting aberrations favourably. When, for example, a lens system having the focal length of 35 mm and film size of 24 .times. 36 mm is arranged so that it can be shifted by 11 mm in the diagonal direction of image surface, the field angle which should be included by this lens system becomes 84.degree. though the field angle to be included by the ordinary lens system with 35 mm field angle is 64.degree.. This field angle is approximately equal to the field angle of a lens system with the focal length of about 23 mm and film size of 24 .times. 36 mm. To include the field angle of 84.degree. by a lens system with 35 mm focal length, it is necessary to keep the aperture efficiency large and, at the same time, to make the equality of image in the image circle high. It is, however, difficult to obtain such lens system because it is very difficult to correct curvature of field and coma favourably. For known shift lens systems, the equality of image in the marginal portion inevitably decreases when the lens system is shifted.